Microwave amplifier



Jan. 15, 1952 H; v. NEHER 2,582,846

MICROWAVE AMPLIFIER Filed April 19, 1944 ELE; L

58 l ELE- lA 3mm" Patented Jan. 15, 1952 MICROWAVE AMPLIFIERHenryVictor. Neher, Pasadena, Calif., assigner, by mesne assignments, tothe. United States of Americav as represented by the Secretary of theNavy Application April 19, 1944, Serial No, 531,828

25 Claims.

This invention relates to electronic vacuum tubes and particularly to.vacuum tubes having one or more grids .adaptedfor operation at extremelyhigh frequencies.

Construction of vacuum tubes in. accordance with this invention.provides for extremely close spacing between the elements of the vacuumvtube, thus reducing electron. transit time and grid circuit loading andalso provides for built-in resonant cavities of which the electrodesform a part, thereby. avoiding losses and other. undesired effects ofthe conventional leadsof supports of the electrodes. Although the saidresonant cavities are enclosedwithin the4 vacuum system of the vacuumtube, means are. provided for tuning them from the outside. An alternateform of cathode may also be provided which is adaptedv to reducevdiiiiculties arising from heating of the grids. Among the objects of theinvention, therefore, are the production of a vacuum tube capable ofproviding amplification at extremely high frequencies, such as about3,000.megacycles, the provision of very close spacing between theelectrodes of such vacuum tube, the provision of resonant cavities intowhich the electrodes are built to minimize lead reactances and losses,and the provision of means for tuning such a vacuum tube.

The. invention will. be. explained in connection with the drawing, inwhich Fig. l is a longitudinal cross section, broken off at the top andbottom. of the vacuum tube in accordance with the present invention;Eig. 1A is a fragmentary seciionr view of a tube of the type shown inFig. 1, but having a plurality of grids; andy Fig. 2 is a longitudinalcross section of a form of cathode particularly adapted for use in anVimproved part of a vacuum tube. in accordance with this in- Vention.

As will be seen from Fig. l, a distinguishing feature of this type ofvacuum tube is that its elements are formed chiefly of. two opposedquarter-wave coaxial resonators 5 and 6, the opposite and neighboringextremities oi the central columns of which form the cathode and theanode respectively, the two resonators being separated by a small spacein which one or. more grids, such as the grid 'I- may be located. Thevacuum tube may conveniently be constructed by iirst building the anoderesonator assembly and the cathode resonator assembly and putting eachtogether separately, then fitting these together with one or more gridsand spacers and securing the electrode structure together, thenenclosing the electrode structure. in a steel shell such as the steelshell used for making metal vacuum tubes oi the type 6L6, provided with`the usual base, which basemay previously have been. attached to thecathode assembly, then inserting the input and output transmission linesthrough the steel shell tothe. electrode assembly and sealing theselines to the. steel shell, and finally evacuating and seal.- ing thesteel shell. The. forms of construction which facilitate this type oivassembly constitute the important features oi this invention.

The anode resonator G is formed by a metallic cylinder illA which may beof copper, a flexible diaphragm, preferably oi copper, showny at II. anda copper cylinder I2 having4 a reduced lower portion I3. the lowersurfaceof which is the, effectiveanode surface of the vacuum tube. Thereis alsdan inward iiange III.A mounted on the lower end of the cylinderin. The central portion of the. anode surface is formed by the`extremities of an Invar rod I5, which is securely fastened, as by.soldering or welding tothe reduced portion i3` of thecopperstructure I2.

The, cylinder I0 is mounted snugly in another cylinder ilv from` whichit is insulated by a thin layer of insulation shown at I8 and` I9. Thisinsulation is preferably thin mica. Thus the en tire, anode resonatorisv insulated from the rest Of the structure of the vacuumy tube and maybe maintained at anode potential. The elimination of by-,pass condenserstructure within the resonant circuit of the resonator itself providesan important reduction of losses the device. The surfaces oilthe'cylindersA IQ and I`I are close together overa sufficient area toprovide good heat conduction away from the anode.

When the vacuum tube is assembled, the cylinder I'I is in a liftedposition with respect to the outer steel shell 2G. The cylinder It islikewise maintained; in such a fixed position. The cylinder l'l isprovided with upper and lower anges 2 I and 22 extending toward theshell 2li. On the upper flange 2l, are mounted two struts 24 and 25,from the junction of which is mounted, by meansv of a rod 2t, aninsulated fixed coupling with the Invar rod I5, the` said xed couplingincluding a metal cup 2l and a ceramic insulator 28 cemented both to therod I5, and to the cup 2i. Preferably struts 2!!` and 25 are sopositioned that the junctions of these struts with flange 2I and thejunction of these struts with each other lie substantially within aplane including the axis of resonator. 6. If now the shell 20 issqueezed in the plane of the struts 24 and 25, the junction of thesestruts will be pushed upward and the rod I5 will thereby be lifted,pulling the anode away from the grid and cathode. and thereby decreasingthe loading capacitance across the resonator and raising the naturalfrequency of the resonator. In this operation the mechanical deformationis taken up by flexing of the diaphragm I I. The importance of the useof Invar as a material for the rod I5 is shown by the fact that when theanode becomes heated because of the operation of the vacuum tube, theconsequent expansion of the copper cylinder I2 will cause the diaphragmI I to flex without, however, changing the position of the anode. Theslight change in the volume of the resonator thus produced will have asubstantially insignificant effect upon the resonator frequency, aresonator of this type being more sensitive to changes in capacitance atlocations of maximum electric iields than to slight changes in volume.

If squeezing pressure on the shell 20 in the plane of the struts 24 and25 is released, or if the shell 20 is squeezed in a plane at rightangles to the plane of the struts 24 and 25, the junction of thesestruts will be pulled down and the position of the anode will likewisebe pushed down, thereby lowering the natural frequency of the resonator6. In order to facilitate the application of squeezing pressures of thetypes described upon the shell 20, a clamping ring 30 is provided aroundthe outside of the shell 20 at an appropriate place and a screw 3| isthreaded in this ring in a position adapted to squeeze the shell 20 inthe plane of the struts 24 and 25. Another screw is provided 90 awayaround the circumference of the clamping ring 30 for obtaining squeezingin the other dimensions. Each screw cooperates with a stud such as thestud 32 mounted on the clamping ring 30 at a position opposite thescrew. Other forms of squeezing mechanism might be provided instead, ifdesired.

Output coupling from the anode resonator 5 is provided by the loop 35connected to the coaxial conductor transmission line 36. Thetransmission line 36 is mounted on the shell 20 and the cylinder I1 butis not in electrical contact with the anode resonator, passing through ahole in the wall of the cylinder I which leaves y a slight clearancebetween the cylinder I0 and the outer conductor of the transmission line36. In order to maintain the vacuum in the apparatus, the outerconductor of the transmission line 35 is sealed to the shell 20 by agas-tight joint. A seal is also provided between the inner and outerconductors of the transmission line 36. This seal is of the usualglass-to-metal type and is not shown on Fig. l, the transmission line 36being broken off. If' desired this seal may be provided at the extremityof the transmission line 36 which is coupled to the resonator Thecathode resonator comprises a metal cylinder 38, preferably maoleV ofcopper, an outward flange 39 at the lower extremity thereof, a flexiblediaphragm 40, an inner copper cylinder 4I and the upper extremity 42 ofthe cathode structure which is mounted within the copper cylinder 4I.The cathode structure is tubular in form with a disk-like end surface 43the upper surface of which is coated with a suitable electron-emittingmaterial adapted to emit electrons when heated. A heater` 68 is providedwithin the structure in the usual way. An upper flange 44 is alsoprovided at the upper end of the cylinder 38 in order to facilitatemounting of the resonator 5 and assembly of these tubes. The upperflange 44 is mounted at its upper edge on an outer cylinder 45 thefunctions of which are structural rather than electrical. Extensivestructure by means of the rod 50.

4 portions of the cylinder 45 are cut away as shown at 46 and 4l, inorder to provide access during construction of these tubes to the meansfor valigning the resonators '5 and 6 and the grid structure orstructures.

When the tube is assembled, the outer cylinder 45 is fixed in relationto the outer shell 20. It is provided with outward flanges at top andbottom, on the latter of which are mounted two struts 48 and 4S thejunction of which is adapted to control the vertical position of thecathode The operation of this strut 43 and 49 is essentially similar tothat of the strut 24 and 25. A clamping ring 5I is provided in theneighborhood of the strut 48 and 4S to facilitate their actuation inpractice. The tuning of the resonator 5 operates in the same manner asthat of the resonator 6, except that an additional effect may be presenton account of the fact that the flexing of the diaphragm 4S, by changingthe narrow spaces between flange 39 and the diaphragm 40 may produce anadditional effect 4from the natural period of the resonator, which maybe expected to be in the same sense as the change produced by thevariation of the capacitance across the open end of the resonator.

Since, as shown below, the grid may be operated at a potential otherthan ground potential, the cathode resonator may be grounded. The inputtransmission line 53 may then be brought into direct electrical contactwith the cylinder 38 of the resonator 5 and, because a relatively largedegree of coupling between the input and the resonator 5 has been foundto be desirable, the inner conductor of the transmission line 53 may bedirectly connected to the inner cylinder 4I, as shown on Fig. 1, bymeans of the small tube 54 which is adapted to engage the innerconductor of the transmission line 53 in a circumferential ring contact.To provide spring contact, oneA or more slots not shown may be cutlongitudinally in the tube '54 near its left hand extremity. Like thetransmission line 35, the transmission line 53 is provided with a vacuumseal, not shown on Fig. 1, between the inner and outer conductor and,likewise, the outer conductor is sealed in a gas-tight manner to theshell 20.

The cylinder 45 is provided, on its lower flange, with a number ofsupports such as those shown at 55 and 55 which are adapted to hold thesaid cylinder in fixed relation to the base of the vacuum tube. Thebase, resonators and grid structure may be assembled as a unit and theelectrode connections brought out to base pins before the steel shell 2%is fitted over the assembly.

The electrodes of the vacuum tube of this invention are of the parallelplane type, which is particularly well adapted for very close spacing.In Fig. 1 a single grid l is shown interposed between the cathode andanode. The grid I is formed of a mesh of very ne wires mounted on acentral aperture of a thin metal disk 58.

Wires of a diameter of .0003 spaced .001" apart are preferred. Thecathode resonator is designed so that the grid will be about .001 fromthe cathode when the resonator is tuned to the desired frequency. Thesmall size of the grid wires is important, because it tends to preventtoo great a spread in transit times of the emitted electrons when thecathode-grid spacing is small. The disk 58 is sandwiched in between thinmica sheets 59 and 50 which serve to insulate it respectively from theresonator 6 and the resonator 5. yThe ilange I4 of the resonator 6, theilange and the mica spacing-disks59and 60^areall provided with aplurality'of perforations which aredesigned-to be brought into alignmentto for-m holes such as that shown at 62. Thereare a nurnber of these,for instance, Isix orV eightv at about the same radial distance from thecenterof the various pieces. -There is also an outer row of perforationsadapted to receive machine screws such as screws 63v and 641v which arethreaded into the flange 22' and which hold the electrode assemblytogether. is used for providing an electrical connection to the grid, asby the pin 65 andthe wire 66, connected to one of the base pins of thevacuum tube which serves as a grid terminal; Itv is to be noted that theouter perforations in the disk 58 are suiciently wide to avoid contactwith the screws 63 and 64'.

Ifr desired, more than one grid' may be provided' in the manner shown inFig. 1A, the grids 58"' and 58' being separated by a mica spacer 59similar to the Ispacing disks 59 and`60 andthe upper and' lower gridsbeing separated by similar spacers from the resonators 5 and 6respectively. In practice it is found that the addition of a screen gridimproves operation by reducing tendencies the tube may have to go intooscillation. In assembling the tube, the metal disk or disks carryingthe grid or grids are assembled with the mica spacers serving toinsulate them as aforesaid andare aligned by the use of temporary pinspassing through the inner seriesof perforations. The aligning sdesirable in order to assure that the grids are properly centered. Thegrid and spacer sandwich is then insertedl between the resonators 5 and5 with the aligning pins passing through the perforations in the angesof the resonators and the screws 6 3, 64, etc., are then inserted in theouter perforations and fastened down. Thereafter, the temporary pinswhich served'to align the grids and spacers may be removed through thelarge apertures 46 and 41 in the cylinder 45. The grid connection pin 65may then. be connected with, one of` the base, pin terminals through asuitable wire 66 and likewise the anode cylinder l2 may be connectedwith another of the base pins through another wire, indicated generallyat 61. The presence of these wires is shown at Fig. 1 in a purelydiagrammatic fashion, it being understood that in actual practiceinsulating bushings would be provided where such wires pass near Votherconducting structures and so on. The heater 68 and the wires connectingthereto, shown at 69 and 10, are likewise indicated in Fig. l, in adiagrammatic fashion for purpose of simplicity.

,v It will be observed that when the resonators 5. and 6 are tuned,` thegrid-cathode spacing"` and the grid-anode spacing will be varied, whichmeans that the amount of grid-loading effect, the transit time and theamplification factor may be varied within a small range during thetuning proce-ss. These effects, however, are extremely small, only avery small movement of the cathode or anode surfaces being necessary fortuning. It is to be; understood that the tuning range of the vacuum tubeof this invention is relatively narrow and the device is intended to bebuilt for service at frequencies. very close to. a particular designfrequency. The tuning range is ample for following the frequency driftof transmitting ape paratus within a reasonable range, for instance, andindeedl it is sufficient for a number of other purposes also. Because ofthe extremely close One ofthe inner perforations spacing-of theelementspossble withvv this typeof. construction, itis possible toobtain radio-fre-V quency amplification at very high` frequencies withthis device.

ciesof about 3000 mc./sec.

It will be noted that the cathode-grid resonator has alower Q than theanode circuit resonator.

This isv desirable because` thegrid= circuit is to small, about 3 squaremillimeters is a conven-Y ient area, in order to reducelthenumberofelectrons which. start out towards the grid and thenreturn tothecathode- The noise effect of such electrons upon the circuits of thetubecanA be reduced by removing` the cathode properfrom the grid andprovidingl a virtual cathode near the grid. in the manner shown in- Fig.2.

Fig. 2 shows a form of cathode adaptedl for use in an improved form forvacuum tube otherwise constructed inv accordance with Fig. 1. Therepresentationof Fig. 2 is ona larger scale than Fig. 1 in order to showdetails of' construction. The cathodey proper is provided by a coatinglof material adapted to emit electrons when heated, which coating isshown at 10, on the end of a cylinder 1| which encloses a suitableheaterand electrical connection therefore, indicated generally by a dottedline. The cylinder 1l is mounted within an outer cylinder 12- and spacedtherefrom by a cylinder or bead 13 of insulating material. The cylinder12 extends upward beyondv the end of the cylinder 1I to provide anenclosure for the4 end of the cylinder 1| and the cathode surface 10,which enclosure is open at the top of 14, the upper part of the cylinder12 being preferably slightly constricted. If desired, grid wires mightbe provided across the opening. 14 in order to assure that the electricfield gradient is perpendicular tothe opening Over a small area. Evenwithout such grid wires, however, a substantially plane virtual cathodeis formed at the opening. It is to be noted that the chamber between thecathode surface 10 and the opening 1 4 is also provided with an annulardisk 15 having a relatively large central openingthe disk'15 serving asan accelerating or focusing electrode and in part as an additional heatshield and assisting the upper end ofthe cylinder 12 in reducing thetendency of the heat dissipated at the cathode to cause the wires of thegrid to be heated.

The metallic cylinder 1I and the cathode surface 1,0 provided thereonare, by virtue of being insulated from the cylinder 12, adapted to beplaced at a potential` more negative than that of the cylinder 12 sothat the annular disk 15 and the rconstricted cylinders 12 will exert anelec? tricaccelerating forcein the direction of thev anode on theelectrons emitted by theA cathode 10. At the virtual cathode provided atthe opening 14, therefore, the electrons will already have somervelocity toward the anode. Under such conditions the possibility ispresented of obtaining a relatively high mutual conductance.

An important reason for the advantage-ofv the Power amplification of theorder of 15-20vdb has been obtainedl at frequen.

cathode of the type shown in Fig. 2 for use in a vacuum tube of the typeshown in Fig. 1 is that with ordinary cathodes the extremely smallspacing betweenv the cathode and the grid results in a greater tendencyfor the grid temperature to rise than occurs in vacuum tubes where thespacing is greater. Increase of grid temperatureinvolves increasedprobability of electron emission from the grids. The extreme proximityof the cathode coating to the grid wires also involves ,some danger ofsputtering some ofv this material onto the grid, so that the heating ofthe grid will involve even greater danger of electron emission. When acathode structure of the type shown in Fig. 2 is used, however, althoughthe virtual cathode provided at the opening 14 remains very close to thegrids, the actual emitting layer 'lll is at a considerable distance fromthe grids, thus reducing sputtering, and the hot portions of the cathodeare likewise removed from the grids, reducing the heating of the grids.It is further to be noticed that the grid-cathode capacitance isA alsoreduced, particularly if no wires are used across the opening 14. Thecathode -structure of the type shown in Fig. 2 is therefore especiallywell adapted to cooperate with a vacuum tube structure of theclose-spaced parallel-plane element type such as that shown in Fig. 1;Because of the reduced scale of Fig. 1, amore conventional cathodestructure, which may also be used in the device of Fig. l, was moreconveniently villustrated there.

' What I desire to claim and obtain by Letters Patent is:

` 1. An electronic tube for very high frequencies comprising opposedcoaxial resonators having opposed parallel plane extremities of theirrespective inner conductors constituting a cathodeand an anoderespectively, with relatively' close spacing, a grid interposed betweensaid extremities and parallel thereto mounted on supporting meansinterposed, together with electrical insulation, between saidresonators, adjustable means for adjusting thelongitudinal position ofsaid extremities including a pair' of struts each mounted `at an"oblique angle 'to the axis of said resonators and having a junctionsubstantially on said axis' mechanically connected to the innerconductorl of 'one vof said resonators, said struts beingadapted'whensqueezed together to pull 'said inner conductor. of saidresonator away from the other of said `vresonators and when pulled apartto propel said inner conductor towards'said other resonator,'said meansincluding' also another pair of struts adaptedto` act similarly'o'n theinner conductor of the other of said resonators,"said resonators 'eachhaving a flexible diaphragm at their respective axial extremitiesfarthest from said grid, said flexible diaphragm being ladapted topermit adjustment of the longitudinal posi'- tion of said innerconductor by said'pair ofstruts, and means, including a tubular metalshell maintaining a desired gas pressure between said extremities and insaid resonators.

2. An electronic tubein accordance with claim 1 having also annularadjustable clamping means externally of said means of maintaining a highvacuum, said clamping means being adapted to push together and to pullapart the struts, through the deformation of the said tubular shell ofsaid vacuum maintaining means.

3. Apparatus in accordance with'claim 1 in which the junction ofthe pairof struts adapted to control the; longitudinal position of the anode ismechanically `.connected to the anode by an Invar rod fastened to theinner conductor of the anode resonator only in the immediateneighborhood of said anode and fastened at its other extremity to thejunction of said struts through an insulated joint.

4. An electronic tube for very high frequencies comprising opposedcoaxial resonators having opposed extremities of their respective innerconductors constituting an anode and a virtual cathode respectively,with relatively close spacing, a grid interposed between saidextremities mounted on supporting means interposed, together withelectrical insulation between said resonators, one of said innerconductors the extremity of which is adapted to operate as a virtualcathode being of hollow construction and including a chamber openingthrough said extremity and being slightly constricted toward saidextremity, a cathode structure including heating means within saidchamber and insulated from said hollow inner conductor in which it issituated, and a diaphragm having a central aperture slightlyconstricting said chamber between said cathode and said extremities,said cathode being adapted to be maintained at a potential moreelectronegative than said hollow inner conductor in which it is locatedand to provide a virtual cathode at the extremity of said innerconductor, means associated with said inner conductors for adjusting thelongitudinal position of said inner conductors of said resonators, andmeans associated with said resonators for coupling electrical circuitsto the respective oscillating elds of each of said resonators.

5. An electron tube for very high frequencies including first and secondclosely spaced electrodes, means for minimizing changes in the spacingof said electrodes due to temperature changes in saidv second electrode,said means comprising rst support means supporting said first electrode,second support means secured to said rst support means and disposedremote from said second electrode, a pair of struts each secured to saidsecond support means at one end of said struts, the other end of saidstruts meeting in a mechanical junction, a rod of a material having athermal coefficient of expansion of substantially zero, said rod beingsecured at one end thereof to the portion of said second electrodenearest said rst electrode, and means securing the other end of said rodto the mechanical junction of said struts.

6. An electron tube for very high frequencies including rst and secondclosely spaced electrodes, said second electrode having the form of ahollow cylinder, means for minimizing changes in the spacing of saidelectrodes due to changes in temperatures of said second electrode, saidmeans comprising, rst support means supporting said first electrode,second support means secured to said first support means and locatedremotely from said electrodes, a pair of struts each secured to saidsecond support means at one end of said struts, the other end of saidstruts meeting in a mechanical junction in alignment with the axis ofsaid second electrode, a rod of material having a thermal coefficient ofexpansion of substantially zero disposed within said second electrode,said rod being secured at one end thereof to the end of said secondelectrode nearest said first electrode and means securing the other endof said rod to said junction of said struts.

7. An electronic tube for very high frequencies comprising opposedcoaxial resonators having opposed parallel plane extremities of theirrespective inner conductors constituting a cathode and an anode,respectively, with relatively close spacing, a grid interposed Ibetweensaid extremities and parallel thereto, mounted on supporting meansinterposed together with electrical insulation between said resonators,adjustable means for adjusting the longitudinal position of saidextremities including a pair of struts each mounted at an oblique angleto the axis of said resonators and each mechanically connected to theinner conductor of one of said resonators, said struts being adaptedwhen squeezed together to pull said `inner conductor of said resonatoraway from the other of said resonators and when pulled apart to propelsaid inner conductor tolward said other resonators.

Lconductor of one of said resonators, said struts being adapted whensqueezed together to pull said conductor of said resonator away from theother vof said resonators and when pulled apart to propel said innerconductor toward said other resonator, one of said resonators having aflexible 4diaphragm Iat the axial extremity 'farthest from said grid,said exible diaphragm being adapted to permit adjustment of thelongitudinal position of said inner `conductor by said pair of struts.

9. vAn electronic tube for very high frequencies comprising opposedcoaxial resonators having opposed parallel plane extremities of theirrespective inner conductors constituting a cathode and an anode,respectively, with relatively close spacing; va plurality of gridsinterposed between said extremities and parallel thereto mounted onsupporting means 'interposed together with electrical linsulationbetween. said resonators, adjustable means associated with one of saidinner conduc- -tors for adjusting the longitudinal position of saidextremities, including a pair of struts, each mounted Vatan obliqueangle to the axis of said resonators and having a junction substantiallyon said axis mechanically connected to the inner `vconductor of one ofsaid resonators, said struts being adapted when squeezed together topull said inner'conductor of said resonator away from "the other of saidresonators and when pulled Iapart to propel said inner conductor towardthe other of said resonators.

10. An electronic tube for very high frequencies, comprising opposedcoaxial resonators havving opposed parallel plane extremities of theirrespective inner conductors constituting a cathode and an anode,respectively, with relatively `close spacing; a plurality of gridsinterposed between said extremities 'in parallel thereto,

mounted on supporting rneans interposed together with" electricalinsulation between said resonators, adjustable means Iassociated withone of said inner conductors for adjusting the longitudinal vposition ofsaid extremities including a pair of struts, each mounted at an obliqueangle to the axisofA vsaid resonators and having a junctionsubstantially on said'axs, saidjunctionbeing metors having opposedparallel plane extremities of their respective inner conductorsconstituting a cathode and an anode, respectively, with relatively ciosespacing, a plurality of grids interposed between said extremities andparallel thereyto mounted 4on supporting means interposed together withelectrical insulation between said resonators, adjustable meansassociated with said inner conductors for adjusting the longitudinalposition of said extremities including a pair of struts, 'each mountedat an oblique angle to the axis of said resonators and having a junctionsubstantially on said axis mechanically connected to the inner conductorof Vone of said resonators,

said struts being adapted when squeezed together to pull said innerconductor of said resonator away -from the other-of said resonators andwhen pulled apart to propel said inner conductor toward said otherresonator, said means including also another pair of struts adapted toact similarly on the inner conductor of the other of said resonators,said resonators each having a flexible diaphragm at their respectiveaxial extremities furthest from said grids, said flexible diaphragmsbeing ladapted to permit adjustment of the longitudinal `position of-said inner conductors by said pairs of struts, and means including atubular `metal shell surroundingsaid resonators for maintaining a`desired gas pressure between said extremities and in said resonators.

12. An electronic tube lfor very high frequencies, `.comprising opposedcoaxial resonators having opposed extremities of their respective innerconductors -constituting an anode and la Virtual cathode, respectively,with relatively close spacing, a grid interposed between saidextremities mounted -on supporting means interposed together withelectrical insulation between said resonators, one-of said innerconductors, the extremity of which is adapted to operate as a virtualcathode, being of hollow construction and including a chamber openingthrough said extremity and being slightly constricted toward saidextremity, -a Acathode structure including heating means `within saidchamber and insulated lfrom said hollow inner Iconductor in which it ising, adjustable means for adjusting the longitudinal-position of saidextremities, including-a pair of struts, each mounted at an obliqueangle tothe axis of saidresonators and having a junction substantiallyon said axis, and a rod secured at one end thereof to the innerconductor of one van anode, respectively, with relatively close spacing,adjustable means for adjusting the longitudinal position of saidextremities including a pair of struts, each mounted at an oblique angleto-the axis of said resonators and having a junction substantially onthe axis of said resonators,

a rod of a material having a thermal coeiiicient expansion ofsubstantially zero, said rod being secured at one end thereof to .theextremity of one of said inner conductors, means joining the hother endof said rod to said junction of said struts,`and means associated withsaid struts for varying the spacing of the ends of said struts remotefrom said junction whereby the spacing A of said extremities of saidinner conductors is varied.

15. In an electron tube including first and second elements, one oi'said elements being 'rigidly supported, means including a rod ofmaterial having a thermal coeicient of expansion of substantially zerofor maintaining the spacing of said elements constant while the other ofsaid elements undergoes a change in temperature and.

Ymeans including said rod, and a pair of intersecting struts supportingsaid rod for micrometrically'varying the spacing between said twoelements.v

16. An electron tube for very high frequencies f comprising opposedcoaxial resonators having opposed parallel plate extremities of theirrespective inner conductors constituting a cathode and Van anoderespectively with relatively close spacing, a rst one of said resonatorsincluding a conductive wall substantially closing the end of said firstresonator adjacent said second resonator, a grid interposed between saidextremities and 'parallel thereto mounted on a flat, conductivesupporting sheet extending parallel to said conductive wall, a sheet ofelectrical insulation disposed between said conductive wall and saidconductive supporting sheet, and electrical insulating means disposedbetween said conductive supporting sheet land said second resonator.

17.Y An electron tube as in claim 16, said elec- "tron tube furthercomprising means coupled to fs'aid inner conductors for adjusting thelongitudinal position of said extremities.

j 18V. An electron tube as in claim 16, said elec- 1x9, An electronictube for very high frequen- {fcies comprising opposed coaxial resonatorshavjrinrg opposedr parallel ,plate extremities of their --respectiveinner conductors constituting a cathode and an anode respectively withrelatively fclose spacing, a first'one of said resonators infcludi'ng' ametallic wall substantially closing thel 'end'of said first resonatoradjacent the second jA of said resonators, a grid interposed betweensaid extremities and parallel thereto mounted on a at conductivesupporting sheet extending paral- V`-lel to lsaid metallic wall, a firstsheet of electric insulation disposed between said supporting sheet andsaid metallic wall, a second sheet of electrical insulation disposedbetween said supporting sheet and said second resonator, meansassociated with ysaid'inner conductors for adjusting the longitudinalpositions of said extremities and means associated with said coaxialresonators providing a gas tight enclosure surrounding said extremities.20. An electronic tube for very high frequency including a coaxialresonator, the extremity of the Yinner conductor of said resonatoracting as a.

virtual cathode, said inner conductor being of hollow construction andincluding a chamber opening through said extremity and being slightlyconstricted toward said extremity, a cathode structure including heatingmeans within said chamber and insulated from said hollow inner conductorand a diaphragm having a central aperture slightly constricting saidchamber between said cathode and said extremity, said cathode beingadapted to be maintained at a potential more negative than said hollowinner conductor to provide a virtual cathode at the extremity of saidinner conductor.

21. A cathode structure for an electron tube comprising a hollowcylindrical member the extremity of which is adapted to operate as avirtual cathode, said member including a chamber opening through saidextremity and being slightly constricted toward said extremity, acathode including heating means disposed within said Lchamber andelectrically insulated from said cylindrical member, and a diaphragmhaving a. central aperture slightly constricting said chamber betweensaid cathode and said extremity, said structure thereby providing avirtual cathode at said extremity of said cylindrical member when saidcathode is maintained at a potential more negative than said cylindricalmember.

Y22. In a coaxial cavity resonator in which a first end of the innerconductor of said resonator `is disposed in spaced relationship to aiirst end of said resonator, means for varying the spacing between saidfirst end of said inner conductor and said rst end of said resonatorcomprising a pair of intersecting struts each mounted at an obliqueangle to the axis of said resonator and each mechanically connected tothe inner conductor of said resonator, said struts being adapted whensqueezed together to pull said inner conductor of said resonator awayfrom said rst end of said resonator and when pulled apart to propel saidinner conductor toward said rst end of said resonator.

23. In a coaxial cavity resonator in which a first end of the innerconductor of said resonator is disposed in spaced relationship to a rstend of said resonator, means for varying the spacing between said rstend of said inner conductor and said first end of said resonatorcomprising a pair of struts each mounted at an oblique angle rto theaxis of said resonator and having a junction substantially on the axisof said resonator vmechanically connected to said inner conductor,

said struts being adapted when squeezed together --to pull saidinnerconductor of said resonator away froml said first end ofsaidresonator and when pulled apart to propel said inner conductortoward said rst end of said resonator.

i. 24.V In a coaxially cavity resonator in which a first end of theinner conductor of said resonator is disposed in spaced relationship toa rst end of said resonator, means for varying the spacing between saidfirst end of said inner conductor and said first end of said resonatorcomprising,

Va pair of struts each secured at one end to the outer conductor of saidresonator at a second end of said resonator, the other ends of saidstruts meeting in a mechanical junction in align- Ament with the axis ofsaidresonator. a rod dis- 13 posed within said inner conductor, said rodbeing secured at one end to said i'irst end of said inner conductor,said rod being secured at its other end to said junction of said struts.

25. 1n a coaxial cavity resonator in Which a first end of the innerconductor of said resonator is disposed in spaced relationship to afirst end of said resonator, means for varying the spacing between saidiirst end of said inner conductor and said first end of said resonatorcomprising, a pair of struts each secured at one end to the outerconductor of said resonator at a second end of said resonator, thepoints of attachment of said struts being located at the opposite endsof a diameter of said outer conductor, the other ends of said strutsmeeting in a mechanical junction in alignment with the axis of saidresonator, means securing said innerconductor to said junction of saidstruts and means for deforming said 'second end of said resonator in amanner to change the spacing between the points of attachment of saidstruts to said outer conductor, said struts being adapted when squeezedtogether to pull said inner conductor of said resonator away from saidfirst end of said resonator and 'i4 when pulled apart to propel saidinner conductor toward said rst end of said resonator.

HENRY V. NEHER.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,088,722 Potter Aug. 3, 19372,146,365 Batchelor s Feb. 7, 1939 V2,167,201 Dallenbach July 25, 19392,183,215 Dow Dec. 12, 1939 2,251,085 Unk July 29, 1941 2,284,405McArthur May 26, 1942 2,353,742 McArthur July 18, 1944 2,353,743McArthur July 18, 1944 2,396,802 Mouromtsei et al. Mar. 19, 19462,418,844 Le Van Apr. 15, 1947 2,429,760 Hotine Oct. 28, 1947 2,436,700Spielman Feb. 24, 1948 2,446,017 McArthur July 17, 1948 2,445,992 BeggsJuly 27, 1948

